Being able to pass arbitrary data in Replication messages

[cBournhonesque]

I don't know how hard it would be, but I need to maintain a mapping between the RepliconTick and the lightyear Tick.
The only way i've found is to intercept the replicon bytes and add the tick at the start of the bytes, like so: https://github.com/cBournhonesque/lightyear/blob/main/crates/replication/replication/src/checkpoint.rs#L190

That seems pretty hacky; I wonder if there would be a way to provide a hook where users could specify arbitrary data that should be included in the replicon messages.

[Shatur]

Agree, it's pretty hacky. I'll think what we can do.

[Shatur]

It's a resource, right? Maybe just replicate it? We're getting resource replication after Bevy 0.19.

[cBournhonesque]

Are you suggesting that I just replicate the lightyear Tick as a resource?
But what if 3 messages are sent for a given RepliconTick, and the resource is only included on the third one? Then I wouldn't be able to know the mapping until I receive the 3rd message.

[Shatur]

Ah, right, this won't work 🤔

[Shatur]

Do I understand correctly that you can't easily map your tick to the one in Replicon because you speed up and slow down?
Mapping would be ideal since it saves traffic...

We can support what you're asking by creating a special resource that holds Vec<u8>, and if it's not empty, include it inside each message. On the client, we'll read these bytes and provide them inside contexts as Vec<u8>. Would that work for you?

For update messages, we have flags in the header that tell us what's inside the message:

bevy_replicon/src/shared/replication/update_message_flags.rs

Lines 9 to 14 in b21bcd5

	pub(crate) struct UpdateMessageFlags: u8 {
	const MAPPINGS = 0b00000001;
	const DESPAWNS = 0b00000010;
	const REMOVALS = 0b00000100;
	const CHANGES = 0b00001000;
	}

So adding USERDATA will have zero cost if you don't use it.

However, mutate messages only have a list of entities, so this will require adding an extra byte that tells whether the user data is present.